The disclosure of Japanese Patent Application No. HEI 11-359022 filed on Dec. 17, 1999 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to hard particles, a wear resistant iron-based sintered alloy, and a method of producing the alloy. The invention further relates to a valve seat formed from the sintered alloy, and a cylinder head including a valve seat or valve seats formed from the sintered alloy. The valve seat is suitably used in a gas engine using LPG, CNG, or like gas as a fuel.
2. State of the Art
In the discussion of the state of the art that follows, reference is made to certain structures and/or methods. However, the following references should not be construed as an admission that these structures and/or methods constitute prior art. Applicant expressly reserves the right to demonstrate that such structures and/or methods do not qualify as prior art against the present invention.
Laid-Open Patent Publication (Kokai) No. SHO 53-112206 of Japanese Patent Application (published in 1978) discloses, as a wear resistant sintered alloy for use in forming a valve seat or the like, a sintered alloy obtained by forming a green compact from a mixed powder. The mixed powder is obtained by mixing a parent material having a composition of a low-alloy steel or a stainless steel with 5-40% of a powder of hard particles, and then sintering the green compact at 1050-1250xc2x0 C. The hard particles have a composition of 0.10% or less of Carbon (C), 0.5-10% of Silicon (Si), 0.40% or less of Manganese (Mn), and 10-50% of Molybdenum (Mo), as basic elements, and a total of 40% of at least one element selected from Nickel (Ni), Chromium (Cr) and Cobalt (Co), and a balance consisting of Iron (Fe).
In the aforementioned sintered alloy, the amount of Mn contained in the hard particle is relatively small, that is, 0.40% or less.
Additionally, in order to ensure improved durability of a sintered alloy, it is preferable to provide increased strength of adhesion between the hard particles and the base or parent material. However, in the aforementioned sintered alloy the adhesion strength between the hard particles and the base is not sufficiently high, and can be further improved.
The invention was developed in the light of the above-mentioned circumstances. It is therefore an object of the invention to provide hard particles, a wear resistant iron-based sintered alloy, a method of producing a wear resistant iron-based sintered alloy, and a valve seat, which assure increased adhesion strength between the hard particles and the base, a sufficiently high density of the sintered alloy, and a good solid lubrication property due to the use of Mo.
The hard particles have a composition of 20 to 70% of Mo, 0.5 to 3% of C, 5 to 40% of Ni, 1 to 20% of Mn, a balance of Fe, and impurities (mass %). The particle may also comprises 40% or less of Co.
Alternatively, a hard particle may have a composition of 20 to 60% of Mo, 0.2 to 3% of C, 5 to 40% of Ni, 1 to 15% of Mn, 0.1 to 10% of Cr, a balance of Fe, and impurities (mass %). The particle may also comprise at least one of 40% or less of Co and 4% or less of Si.
A wear-resistant iron-based sintered alloy has two components: a base and a plurality of particles. The base has the composition 0.2 to 5% of C, 0.1 to 12% of Mn, a balance of Fe, and impurities (mass % of the base) and the hard particles, dispersed in the base with an area ratio of 10 to 60%, have the composition 20 to 70% of Mo, 0.5 to 3% of C, 5 to 40% of Ni, 1 to 20% of Mn, a balance of Fe, and impurities (mass % of the particles). After sintering, the alloy has the composition 4 to 30% of Mo, 0.2 to 3% of C, 1 to 20% of Ni, 0.5 to 12% of Mn, a balance of Fe, and impurities (mass % of the alloy).
Similarly, an alternative wear-resistant iron-based sintered alloy has two components: a base and a plurality of particles. The base has the composition 0.2 to 5% of C, 0.1 to 10% of Mn, a balance of Fe, and impurities (mass % of the base)and the hard particles, dispersed in the base with an area ratio of 10 to 60%, 20 to 60% of Mo, 0.2 to 3% of C, 5 to 40% of Ni, 1 to 15% of Mn, 0.1 to 10% of Cr, a balance of Fe, and impurities (mass % of the particles). After sintering, the alloy has the composition 4 to 30% of Mo, 0.2 to 3% of C, 1 to 20% of Ni, 0.5 to 9% of Mn, 0.05 to 5% of Cr, a balance of Fe, and impurities (mass % of the alloy).
A method is provided whereby powders of the alloys and hard particles of the present invention are mixed (with a small amount of carbon), compacted, and sintered into wear resistant alloys.